Magnetic storage systems store information by magnetizing bit positions on tracks located on a surface of a magnetic media, e.g. a magnetic disk. An actuator arm supports and maintains a Magneto-Resistive (MR) head close to the magnetic disk surface to perform the read and write operations on the disk surface. As the magnetic disk is moved past the MR head, the variations in the magnetic flux passing through the MR head result in changes in the electrical resistance of the MR head.
An MR head is biased with a constant electrical current so that a voltage is present across the MR head. A preamplifier is then used to detect changes in the voltage across the MR head caused by the variations in the electrical resistance of the MR head. Changes in the voltage across the MR head are used to extract the data stored on the magnetic disk surface.
Recently, such MR heads have been used in drastically smaller disk drives. In such environment, the foregoing preamplifiers must have low power requirements and exhibit low intrinsic noise, while providing high-bandwidth operation. This is conventionally accomplished by using large field effect transistors (FETs). Unfortunately, such arrangements exhibit high capacitance which in turn results in a lack of sufficient bandwidth.
Moreover, prior art preamplifier applications are often subject to high levels of low-frequency extrinsic noise resulting from the circuit environment, i.e. hardware, moving head, etc., that is common in many applications of smaller disk drives. Unfortunately, the prior art FETs fail to sufficiently filter such low-frequency extrinsic noise.
There is thus a need for a preamplifier design that exhibits low intrinsic noise and sufficiently filters extrinsic low-frequency noise, while providing high-bandwidth operation.